1. Field of the Invention
The present invention relates to a solution circulation type metal-halogen battery, and more particularly to a solution circulation type-halogen battery wherein the flow rate and the velocity distribution of an electrolyte flowing through a reaction tank are equalized.
2. Description of the Prior Art
As conventional metal-halogen batteries, a zinc-bromine secondary battery and a zinc-chlorine secondary battery are known. In such a secondary battery, single cells are connected to each other in series or parallel, as required, so as to obtain a practical voltage and current. These secondary batteries are frequently used as bipolar-type layer-built batteries as well.
The basic principle of the aforementioned metal-halogen battery will be explained with reference to FIG. 3.
In FIG. 3, a cathode 12 and an anode 14 in a reaction tank 10 are partitioned into a cathode chamber 10a and an anode chamber 10b by means of a separator 16. Electrolyte circulation passages are formed to connect the reaction tank 10, an anolyte storage tank 18, and a catholyte storage tank 20 by means of pipes 22. In this case, the electrolyte flowing through the pipes 22 is pressure-fed to the reaction tank by means of pumps 24a and 24b.
Furthermore, in the reaction tank during charge, halogen is generated on the cathode side, while metal is deposited on the anode side.
At the time of discharge, the metal deposited on an anode side is oxidated and dissolved in the form of metallic ions in the electrolyte, while halogen in the electrolyte is reduced and dissolved in the form of halogen ions in the electrolyte.
FIG. 4 is an exploded view of a conventional electrolyte circulation type layer-built secondary battery based on the above-described principle.
In FIG. 4, an electrode plate 26 is constituted by an insulating portion 28 and a conductive portion 30, and manifolds 32 are provided on a diagonal thereof. In addition, the separator 34 has a separator frame 36 in the periphery of a separator membrane 34a, and manifolds 38 and channels 40, which supply the electrolyte to the cathode chamber and the anode chamber, are formed in the separator frame 36.
Thus, in a metal-halogen battery, the electrolyte circulates through the passages where the electrolyte flows from the electrolyte tank, passes each chamber of a cell stack, and returns to the electrolyte tank. However, since the electrolyte flows through the cathode and anode chambers with a thickness of 1 mm or thereabout in the layered plate, an overvoltage or non-uniform electrodeposition may occur unless the flow in each chamber is uniform, thereby presenting an undesirable situation for the battery.
Furthermore, in view of the need to prevent a shunt current, the inlet and outlet of the electrolyte are conventionally provided on the upper and lower corners of a cell such as to be disposed on a diagonal, as shown in FIG. 4. In addition, if the area of the conductive portion 30 of the electrode becomes large in the order of 600 to 1,200 cm.sup.2, it has been difficult to cause the electrolyte to flow uniformly.
As a means of solving this problem, there has been suggested a metal-halogen battery in which a group of rectifying plates 42 are formed between the channel 40 and the separator membrane 31a, as shown in FIG. 5. This arrangement allows a uniform distribution of the velocity and flow rate of the electrolyte in the respective cathode and anode chambers.
However, the prior art has had the following drawbacks.
First, conventional groups of rectifying plates are constituted by a plurality of rows of rectifying plates, as shown in FIG. 5, because of the difficulty to effect rectification in such a manner as to obtain a uniform distribution of the velocity.
If the groups of rectifying plates 42 are thus constituted by the plurality of rows of rectifying plates, the vertical width of the rectifying plates becomes large. Consequently, there has been a problem in that such a battery is unsuitable for use in an electric vehicle or a forklift for which a battery with a low height, when mounted thereon, is preferred.
In addition, if the groups of rectifying plates 42 are constituted by the plurality of rows of rectifying plates, gas may be retained between the plurality of rows, and this gas serves as a factor in impeding the flow of the electrolyte.
Secondly, the conventional groups of rectifying plates 42 are formed integrally with the separator frame or an electrode frame. Moreover, the structure of the groups of rectifying plates 42 has been very complicated. For these reasons, there has been a drawback since a large amount of processing is involved in the production of the separator frame or electrode frame.